1. Field of the Invention
The present invention relates to methods and devices for detecting the activation of an audible smoke detector alarm.
2. Background of the Technology
During a fire, the occupants of a building may only have a few minutes to escape without harm. Due to the potentially small escape time, it is imperative to give ample warning to the occupants of a burning building. Most devices sold by the fire safety industry rely on audible alarms to alert the occupants in a residential building. Unfortunately, these devices do not help the hearing impaired. Thus, a need arises for a device that provides ample protection for the hearing-impaired in case of a fire emergency.
Known in the art are devices that use visual signals to alert the hearing-impaired of a fire emergency. Examples of such devices are described in U.S. Pat. Nos. 4,227,191 and 4,287,509. These devices combine a detector and a visual alarm in a single device. Another visual warning device is disclosed in U.S. Pat. No. 5,012,223. This device detects the sound from a remote smoke detector and activates a light in response thereto. Visual alarm devices such as these suffer from the serious drawback of being ineffective in alerting a hearing-impaired individual who is asleep.
To address this need, systems combining tactile stimulation (e.g., vibrators and bed shakers) have been proposed. One such device is described in U.S. Pat. No. 4,380,759. This device includes a vibration sensor that is placed next to a smoke detector. When the smoke detector activates, the vibration from the audible alarm triggers a vibrating reed that causes a mild sensation on the skin. Devices such as this are cumbersome to use (especially when the device will only be used at a location temporarily, as in a hotel room) as the user must place the transmitting unit in physical contact with the smoke detector, which is often on a ceiling or otherwise difficult to reach. Other devices for the hearing impaired (e.g., the device disclosed in U.S. Pat. No. 5,917,420) involve the transmission of signals from a detector to a furniture shaker or other tactile stimulation device. While devices such as these are a step in the right direction, they are usually quite expensive and, more importantly, require special hardware.
U.S. Pat. No. 5,651,070 describes a warning device that “listens” for sounds made by devices such as doorbells and smoke detectors and activates a tactile stimulation device in the form of a wrist-watch. This device records a desired audio alarm and continually compares the recorded alarm to ambient sounds picked up from a microphone. A 4 bit comparator is used to declare a match. What criteria are input to the comparator to declare a match is not disclosed. Additionally, this device is burdensome to use in that it requires the user to record the desired sound prior to use. This can be a problem, for example, when a person enters a hotel room late at night because activation of the smoke detector alarm for the purpose of making the recording may disturb other guests.
In addition to the above considerations, false alarm performance is an important consideration in devices such as these. It is a relatively simple matter to detect the activation of a smoke detector audible alarm; it is an entirely different matter to be able to detect such an alarm without falsely detecting other devices commonly found in the home. Such devices may produce constant broadband noise (e.g., vacuum cleaners and blenders) or may produce intermittent sounds at well defined frequencies at or near the frequency of a smoke detector alarm (e.g., alarm clocks, telephones, cell phones, etc.). It is well known that users quickly learn to ignore an alarm device that is prone to excessive false alarms, thereby rendering such a device useless.